An apparatus is described for measurement of the acoustic impedance of the middle ear at the tympanic membrane. The measuring technique offers a possibility of studying the fine structure of the middle ear impedance, which contains not a single but several resonance peaks. The method employed makes use of a constant current sound source mechanically fixed to a microphone probe indicator. Both the sound generator and the sound receiver microphone are coupled to a tube which is inserted into the ear. This unit can be fixed directly to the subject's head, thereby eliminating the effect of the subject's movements on the measurements. The results of measurements on eight normal subjects are presented, in part as impedance, in part as admittance. The admittance is measured for 50 cps intervals in the frequency range from 200 to 2000 cps. The individual spread of data proved to be very great and appreciably greater than the difference between the two ears of a single individual.
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Aage R. Møller (1960) studied this question.